"Our study shows that these animals can contribute far more as a tourism resource than as a catch target," he says in a statement.

Sharks have reigned at the top of the ocean food chain for hundreds of millions of years.

But because they mature slowly and produce few offspring, the consummate marine predators have proven vulnerable to industrial-scale fishing.

Tens of millions of the coastal and open-water sharks are harvested every year to supply a burgeoning appetite for meat and especially shark-fin soup.

The researchers found that the annual value to the Palau tourism industry of an individual reef shark at one of the country's major scuba-diving sites is $163,000 a year, or about $1.7 million over the animal's lifetime.

Shark diving accounts for about 80 per cent of the tiny country's GDP and 14 per cent of its business tax base. It also generates more than a million dollars annually in salaries.

In 2009, Palau became the first country in the world to declare all of its territorial waters to be a shark sanctuary, followed last year by Honduras and The Maldives.

Hawaii, the territories of Guam and the Northern Marianas, and the Republic of the Marshall Islands have all banned the possession, sale or distribution of shark fins.

"Shark tourism can be a viable economic engine," says Matt Rand, a shark expert at the Washington-based Pew Environment Group, which commissioned the research.

"This study provides a compelling case that can convince more countries to embrace these animals for their benefit to the ocean and their value to a country's financial well-being."

About a third of open-water sharks face extinction, according to the International Union for the Conservation of Nature (IUCN).

Regional studies have shown that when shark populations crash the impact cascades down through the food chain, often in unpredictable and deleterious ways.